Proteins that control the expression of genetic information interact with specific sequences in DNA. We shall cross-link such proteins to their binding sites on DNA. This will reveal close contacts between the RNA polymerase or the CAP fact (the cyclic AMP activator factor) with promoters and the lactose repressor with the lactose operator. We shall use the photochemical activation of BrdU- and BrdC-substituted DNA to create covalent zero-length crosslinks. We wish to identify the disposition of the RNA polymerase subunits along the DNA. For the lactose repressor and the CAP factor, we wish to determine which amino acids in these proteins touch which pyrimidine bases in the sequences of the DNA binding sites. Our goal is to understand the rules governing protein-DNA interactions.